a. C = (1 + 1/√x)[1/(√x +1) + 1/(√x - 1) - 2/(x - 1) (x khác ± 1; x ≥ 0)]
C = (√x + 1)/√x.{1/(√x +1) + 1/(√x -1) - 2/[(√x+1)(√x-1)] }
C = (√x + 1)/√x. (√x - 1 + √ x + 1 - 2)/[(√x+1)(√x-1)]
C = [(√x + 1).(2√x - 2)]/[√x.(√x +1)(√x-1)]
C = [2(√x + 1)(√x - 1)]/[√x.(√x +1)(√x-1)]
C = 2/√x
b. Để C = 3 ⇔ 2/√x = 3 ⇔ √x = 2/3 ⇔ x = 4/9 (Thỏa mãn)